Epinephrine and the genesis of hypertension

Aerobic training increases renal antioxidant defence and reduces angiotensin II levels, mitigating the high mortality in SHR-STZ model

OBJECTVE

The purpose of the research was to investigate the effects of aerobic training on renal function, oxidative stress, intrarenal renin-angiotensin system, and mortality of hypertensive and diabetic (SHR-STZ) rats.

MATERIALS AND METHODS

Blood pressure, creatinine, urea levels, urinary glucose, urine volume, and protein excretion were reduced in trained SHR-STZ rats.

RESULTS

Aerobic training not only attenuated oxidative stress but also elevated the activity of antioxidant enzymes in the kid'ney of SHR-STZ rats. Training increased intrarenal levels of angiotensin-converting enzymes (ACE and ACE2) as well as the neprilysin (NEP) activity, along with decreased intrarenal angiotensin II (Ang II) levels. Aerobic training significantly improved the survival of STZ-SHR rats.

CONCLUSION

The protective role of aerobic training was associated with improvements in the renal antioxidative capacity, reduced urinary protein excretion along with reduced intrarenal Ang II and increased NEP activity. These findings might reflect a better survival under the combined pathological conditions, hypertension, and diabetes.

Vasodilatory Effect of Alpinia officinarum Extract in Rat Mesenteric Arteries

Background: Alpinia officinarum (A. officinarum) is known to exhibit a beneficial effect for anti-inflammatory, anti-oxidant, and anti-hyperlipidemic effects. However, no sufficient research data are available on the cardiovascular effect of A. officinarum. Thus, in this study, we investigate whether A. officinarum extract has direct effects on vascular reactivity. Methods: To examine whether A. officinarum extract affects vascular functionality, we measured isometric tension in rat mesenteric resistance arteries using a wire myograph. After arteries were pre-contracted with high-K⁺ (70 mM), phenylephrine (5 µM), or U46619 (1 µM), A. officinarum extract was treated. Results: A. officinarum extract induced vasodilation in a concentration-dependent manner, and this effect was endothelium independent. To further investigate the mechanism, we incubated arteries in a Ca²⁺-free and high-K⁺ solution, followed by the cumulative addition of CaCl₂ (0.01–2.5 mM) with or without A. officinarum extract (30 µg/mL). Pre-treatment of A. officinarum extract reduced the contractile responses induced by cumulative administration of Ca²⁺, which suggests that extracellular Ca²⁺ influx was inhibited by the treatment of A. officinarum extract. These results were associated with a reduction in phosphorylated MLC₂₀ in VSMCs treated with A. officinarum extract. Furthermore, eucalyptol, an active compound of A. officinarum extract, had a similar effect as A. officinarum extract, which causes vasodilation in mesenteric resistance arteries. Conclusion: A. officinarum extract and its active compound eucalyptol induce concentration-dependent vasodilation in mesenteric resistance arteries. These results suggest that administration of A. officinarum extract could exert beneficial effects to treat high blood pressure.

The abnormalities of adrenomedullary hormonal system in genetic hypertension: Their contribution to altered regulation of blood pressure

It is widely accepted that sympathetic nervous system plays a crucial role in the development of hypertension. On the other hand, the role of adrenal medulla (the adrenomedullary component of the sympathoadrenal system) in the development and maintenance of high blood pressure in man as well as in experimental models of hypertension is still controversial. Spontaneously hypertensive rats (SHR) are the most widely used animal model of human essential hypertension characterized by sympathetic hyperactivity. However, the persistence of moderately elevated blood pressure in SHR subjected to sympathectomy neonatally as well as the resistance of adult SHR to the treatment by sympatholytic drugs suggests that other factors (including enhanced activity of the adrenomedullary hormonal system) are involved in the pathogenesis of hypertension of SHR. This review describes abnormalities in adrenomedullary hormonal system of SHR rats starting with the hyperactivity of brain centers regulating sympathetic outflow, through the exaggerated activation of sympathoadrenal preganglionic neurons, to the local changes in chromaffin cells of adrenal medulla. All the above alterations might contribute to the enhanced release of epinephrine and/or norepinephrine from adrenal medulla. Special attention is paid to the alterations in the expression of genes involved in catecholamine biosynthesis, storage, release, reuptake, degradation and adrenergic receptors in chromaffin cells of SHR. The contribution of the adrenomedullary hormonal system to the development and maintenance of hypertension as well as its importance during stressful conditions is also discussed.

Immunosuppression of Macrophages Underlies the Cardioprotective Effects of CST (Catestatin)

[Figure: see text].

From Brain to Blood Vessel: Insights From Muscle Sympathetic Nerve Recordings: Arthur C. Corcoran Memorial Lecture 2020

Multiunit recordings of postganglionic sympathetic outflow to muscle yield otherwise imperceptible insights into sympathetic neural modulation of human vascular resistance and blood pressure. This Corcoran Lecture will illustrate the utility of microneurography to investigate neurogenic cardiovascular regulation; review data concerning muscle sympathetic nerve activity of women and men with normal and high blood pressure; explore 2 concepts, central upregulation of muscle sympathetic outflow and cortical autonomic neuroplasticity; present sleep apnea as an imperfect model of neurogenic hypertension; and expose the paradox of sympathetic excitation without hypertension. In awake healthy normotensive individuals, resting muscle sympathetic nerve activity increases with age, sleep fragmentation, and obstructive apnea. Its magnitude is not signaled by heart rate. Age-related changes are nonlinear and differ by sex. In men, sympathetic nerve activity increases with age but without relation to their blood pressure, whereas in women, both rise concordantly after age 40. Mean values for muscle sympathetic nerve activity burst incidence are consistently higher in cohorts with hypertension than in matched normotensives, yet women's sympathetic nerve traffic can increase 3-fold between ages 30 and 70 without causing hypertension. Thus, increased sympathetic nerve activity may be necessary but is insufficient for primary hypertension. Moreover, its inhibition does not consistently decrease blood pressure. Despite a half-century of microneurographic research, large gaps remain in our understanding of the content of the sympathetic broadcast from brain to blood vessel and its specific individual consequences for circulatory regulation and cardiovascular, renal, and metabolic risk.

Vasa Vasorum Lumen Narrowing in Brain Vascular Hyalinosis in Systemic Hypertension Patients Who Died of Ischemic Stroke

Ischemic stroke is a major cause of death among patients with systemic hypertension. The narrowing of the lumen of the brain vasculature contributes to the increased incidence of stroke. While hyalinosis represents the major pathological lesions contributing to vascular lumen narrowing and stroke, the pathogenic mechanism of brain vascular hyalinosis has not been well characterized. Thus, the present study examined the postmortem brain vasculature of human patients who died of ischemic stroke due to systemic hypertension. Hematoxylin and eosin staining and immunohistochemistry showed the occurrence of brain vascular hyalinosis with infiltrated plasma proteins along with the narrowing of the vasa vasorum and oxidative stress. Transmission electron microscopy revealed endothelial cell bulge protrusion into the vasa vasorum lumen and the occurrence of endocytosis in the vasa vasorum endothelium. The treatment of cultured microvascular endothelial cells with adrenaline also promoted the formation of the bulge as well as endocytic vesicles. The siRNA knockdown of sortin nexin-9 (a mediator of clathrin-mediated endocytosis) inhibited adrenaline-induced endothelial cell bulge formation. Adrenaline promoted protein-protein interactions between sortin nexin-9 and neural Wiskott–Aldrich syndrome protein (a regulator of actin polymerization). Spontaneously hypertensive stroke-prone rats also exhibited lesions indicative of brain vascular hyalinosis, the endothelial cell protrusion into the lumen of the vasa vasorum, and endocytosis in vasa vasorum endothelial cells. We propose that endocytosis-dependent endothelial cell bulge protrusion narrows the vasa vasorum, resulting in ischemic oxidative damage to cerebral vessels, the formation of hyalinosis, the occurrence of ischemic stroke, and death in systemic hypertension patients.

Neurocardiac regulation: from cardiac mechanisms to novel therapeutic approaches

Cardiac sympathetic overactivity is a well-established contributor to the progression of neurogenic hypertension and heart failure, yet the underlying pathophysiology remains unclear. Recent studies have highlighted the importance of acutely regulated cyclic nucleotides and their effectors in the control of intracellular calcium and exocytosis. Emerging evidence now suggests that a significant component of sympathetic overactivity and enhanced transmission may arise from impaired cyclic nucleotide signalling, resulting from compromised phosphodiesterase activity, as well as alterations in receptor-coupled G-protein activation. In this review, we address some of the key cellular and molecular pathways that contribute to sympathetic overactivity in hypertension and discuss their potential for therapeutic targeting.

Functional Dosage of Muscarinic Cholinergic Receptor 3 Signalling, Not the Gene Dose, Determines Its Hypertension Pathogenesis

BACKGROUND

Multiple quantitative trait loci for blood pressure (BP) have been localized throughout human and rodent genomes. Few of them have been functionally identified especially in humans, and little is known about their pathogenic directionality when identified. We focused on Chrm3 encoding the muscarinic cholinergic receptor 3 (M3R) as the causal gene for C17QTL1 in the Dahl salt-sensitive rat model.

METHODS AND RESULTS

Congenic knock-ins, gene-specific knockout, and ex vivo and in vivo function studies were applied in the Dahl salt-sensitive rat model of polygenic hypertension. A Chrm3 missense T1667C mutation in the last intracellular domain functionally correlated with a rise in BP increased the M3R signalling and resensitization, and adrenal epinephrogenesis. Gene targeting that abolished the M3R function without affecting any of noncoding Chrm3 variants caused a decrease in BP, indicating that the M3R-mediated signalling promotes hypertension. In contrast, removing 8 amino acids from the M3R first extracellular loop had no effect on BP.

CONCLUSIONS

The M3R-specialized signalling constitutes a new pathway of hypertension pathogenesis within the context of a polygenic and quantitative trait. Increased epinephrine in the circulation and secreted from the adrenal glands are suggestive of a molecular mechanism partially mediating M3R to promote hypertension. The structure-function relationships for various M3R domains in their effects on BP pave the way for identifying missense mutations that impact functions on BP as potential diagnostic targets.

Taekwondo training reduces blood catecholamine levels and arterial stiffness in postmenopausal women with stage-2 hypertension: randomized clinical trial

Objective: Menopause is associated with a progressive impairment of vascular function and muscular strength in women. Accordingly, the purpose of this study was to determine if Taekwondo training could improve blood catecholamine levels, arterial stiffness, blood pressure (BP) and skeletal muscle strength in postmenopausal women with stage-2 hypertension. Methods: 20 postmenopausal women (70 ± 4 years old) with stage-2 hypertension were randomly assigned to a 1) Taekwondo training (TT; n = 10) or 2) Control (CON; n = 10) group. Taekwondo training was performed for 60 minutes/day, 3 days/week for 12-weeks. Results: There were significant (P < 0.05) group by time interactions for resting epinephrine (EP) and norepinephrine (NE) levels, with EP decreasing in the TT group and NE increasing in the CON group. Additionally, brachial-ankle pulse wave velocity, resting heart rate, and BP were significantly decreased, while hand grip and leg strength were significantly increased in the TT group compared to CON group. Conclusion: These results suggest that Taekwondo training can be a novel and beneficial mode of exercise for improving cardiovascular function and muscular strength in this population. Abbreviations: TT: Taekwondo training group; CON: control group; EP: epinephrine; NE: norepinephrine; ANS: autonomic nervous system; SNS: sympathetic nervous system; baPWV: brachial-ankle pulse wave velocity.

Neurotransmitter Switching Coupled to β-Adrenergic Signaling in Sympathetic Neurons in Prehypertensive States

Single or combinatorial administration of β-blockers is a mainstay treatment strategy for conditions caused by sympathetic overactivity. Conventional wisdom suggests that the main beneficial effect of β-blockers includes resensitization and restoration of β1-adrenergic signaling pathways in the myocardium, improvements in cardiomyocyte contractility, and reversal of ventricular sensitization. However, emerging evidence indicates that another beneficial effect of β-blockers in disease may reside in sympathetic neurons. We investigated whether β-adrenoceptors are present on postganglionic sympathetic neurons and facilitate neurotransmission in a feed-forward manner. Using a combination of immunocytochemistry, RNA sequencing, Förster resonance energy transfer, and intracellular Ca2+ imaging, we demonstrate the presence of β-adrenoceptors on presynaptic sympathetic neurons in both human and rat stellate ganglia. In diseased neurons from the prehypertensive rat, there was enhanced β-adrenoceptor-mediated signaling predominantly via β2-adrenoceptor activation. Moreover, in human and rat neurons, we identified the presence of the epinephrine-synthesizing enzyme PNMT (phenylethanolamine-N-methyltransferase). Using high-pressure liquid chromatography with electrochemical detection, we measured greater epinephrine content and evoked release from the prehypertensive rat cardiac-stellate ganglia. We conclude that neurotransmitter switching resulting in enhanced epinephrine release, may provide presynaptic positive feedback on β-adrenoceptors to promote further release, that leads to greater postsynaptic excitability in disease, before increases in arterial blood pressure. Targeting neuronal β-adrenoceptor downstream signaling could provide therapeutic opportunity to minimize end-organ damage caused by sympathetic overactivity.

Acute arterial baroreflex-mediated changes in plasma catecholamine concentrations in a chronic rat model of myocardial infarction

While it may be predictable that plasma norepinephrine (NE) concentration changes with efferent sympathetic nerve activity (SNA) in response to baroreceptor pressure inputs, an exact relationship between SNA and plasma NE concentration remains to be quantified in heart failure. We examined acute baroreflex-mediated changes in plasma NE and epinephrine (Epi) concentrations in normal control (NC) rats and rats with myocardial infarction (MI) (n = 6 each). Plasma NE concentration correlated linearly with SNA in the NC group (slope: 2.17 ± 0.26 pg mL(-1) %(-1), intercept: 20.0 ± 18.2 pg mL(-1)) and also in the MI group (slope: 19.20 ± 6.45 pg mL(-1) %(-1), intercept: -239.6 ± 200.0 pg mL(-1)). The slope was approximately nine times higher in the MI than in the NC group (P < 0.01). Plasma Epi concentration positively correlated with SNA in the NC group (slope: 1.65 ± 0.79 pg mL(-1) %(-1), intercept: 115.0 ± 69.5 pg mL(-1)) and also in the MI group (slope: 7.74 ± 2.20 pg mL(-1) %(-1), intercept: 24.7 ± 120.1 pg mL(-1)). The slope was approximately 4.5 times higher in the MI than in the NC group (P < 0.05). Intravenous administration of desipramine (1 mg kg(-1)) significantly increased plasma NE concentration but decreased plasma Epi concentration in both groups, suggesting that neuronal NE uptake had contributed to the reduction in plasma NE concentration. These results indicate that high levels of plasma catecholamine in MI rats were still under the influence of baroreflex-mediated changes in SNA, and may provide additional rationale for applying baroreflex activation therapy in patients with chronic heart failure.

Genetic and Functional Evidence Supports LPAR1 as a Susceptibility Gene for Hypertension

Essential hypertension is a complex disease affected by genetic and environmental factors and serves as a major risk factor for cardiovascular diseases. Serum lysophosphatidic acid correlates with an elevated blood pressure in rats, and lysophosphatidic acid interacts with 6 subtypes of receptors. In this study, we assessed the genetic association of lysophosphatidic acid receptors with essential hypertension by genotyping 28 single-nucleotide polymorphisms from genes encoding for lysophosphatidic acid receptors, LPAR1, LPAR2, LPAR3, LPAR4, LPAR5, and LPAR6 and their flanking sequences, in 3 Han Chinese cohorts consisting of 2630 patients and 3171 controls in total. We identified a single-nucleotide polymorphism, rs531003 in the 3'-flanking genomic region of LPAR1, associated with hypertension (the Bonferroni corrected P=1.09×10(-5), odds ratio [95% confidence interval]=1.23 [1.13-1.33]). The risk allele C of rs531003 is associated with the increased expression of LPAR1 and the susceptibility of hypertension, particularly in those with a shortage of sleep (P=4.73×10(-5), odds ratio [95% confidence interval]=1.75 [1.34-2.28]). We further demonstrated that blood pressure elevation caused by sleep deprivation and phenylephrine-induced vasoconstriction was both diminished in LPAR1-deficient mice. Together, we show that LPAR1 is a novel susceptibility gene for human essential hypertension and that stress, such as shortage of sleep, increases the susceptibility of patients with risk allele to essential hypertension.

Calibration of baroreflex equilibrium diagram based on exogenous pressor agents in chronic heart failure rats

A baroreflex equilibrium diagram describes the relation between input pressure and sympathetic nerve activity (SNA) and that between SNA and arterial pressure (AP). To calibrate the SNA axis (abscissa) of the baroreflex equilibrium diagram, the AP response to intravenous bolus injections of phenylephrine (0.2-50 μg/kg) or norepinephrine (NE, 0.02-5 μg/kg) was examined in normal control rats (NC, n = 9) and rats with chronic heart failure (CHF, n = 6). The maximum slope of the dose-effect curve was significantly smaller in the CHF group than in the NC group (57.3 ± 5.2 vs 80.9 ± 6.3 mmHg/decade for phenylephrine, 60.2 ± 7.8 vs 80.4 ± 5.9 mmHg/decade for NE; P < 0.01). The CHF/NC ratio of the maximum slope was used to calibrate SNA. While the calibrated baroreflex equilibrium diagram showed increased maximum SNA and operating-point SNA in CHF rats compared with NC rats, the magnitude of increase was smaller than that expected from the excess plasma NE concentration in CHF rats. Plasma NE concentration in the CHF group could be disproportionally high relative to SNA.

CATECHOLAMINES AND β2-ADRENOCEPTOR GENE EXPRESSION BEFORE AND AFTER MAXIMAL INCREMENTAL CYCLE TEST IN YOUNG ICE HOCKEY PLAYERS: RELATION TO WORK PERFORMED

The aim of this study was to assess the plasma adrenaline and noradrenaline concentrations as well as whole blood β₂-adrenoceptor gene (ADRB2) expression in young ice hockey players before and immediately after exercise in relation to performed work. Nineteen Youth National Team ice hockey players were subjected to the maximal incremental cycloergometer exercise. The test was done in the pre-competitive phase of training. Among many parameters the plasma adrenaline and noradrenaline concentrations and ADRB2 gene expression in peripheral blood mononuclear cells (PBMC) were determined before and after exercise. The average performed work was 3261.3 ± 558.3 J · kg⁻¹ and maximal oxygen consumption (VO₂max) for all players was 53.85 ± 3.91 mL · kg⁻¹ min⁻¹. The geometric mean of the ADRB2 gene expression was statistically significantly different before and after exercise (P ≤ 0.05), while adrenaline and noradrenaline levels in plasma significantly increased after exercise. In the analysed group of athletes we found that initial level of plasma noradrenaline correlated with the performed work (r = - 0.55, P < 0.014) and normalized ADRB2 expression before the exercise correlated with the work done by them (r = 0.48, P<0.039). However, no statistically significant correlations were found between the plasma adrenaline or noradrenaline concentrations and ADRB2 gene expression in peripheral blood of the players. The performed work in the maximal incremental exercise test of regularly training young ice hockey players depends on the initial levels of noradrenaline in plasma and ADRB2 mRNA in PBMC.

Heritability of Hemodynamic Reactivity to Laboratory Stressors in a Homogenous Arab Population: ‘Oman Family Study’

Background:Exaggerated cardiovascular reactivity to stressful stimuli may be a risk factor for the development of hypertension. The genetic influence on blood pressure (BP) reactivity to stress and its control mechanisms has been receiving considerable support. This study aims at examining the heritability of BP and its intermediate hemodynamic phenotypes to acute stress in a homogeneous Arab population.Methods:Parameters were computed from continuous BP, electrocardiography and impedance cardiography measurements, during rest, word conflict (WCT) and cold pressor (CPT) tests. Heritability estimates (h2) were obtained using the variance components-based approach implemented in the SOLAR software package.Results:Reactivity scores for WCT and CPT increased significantly (P< .05) for systolic (SBP), diastolic (DBP), heart rate (HR), cardiac output (CO), and total peripheral resistance (TPR). They decreased significantly (P< .05) for stroke volume (SV), left ventricular ejection time (LVET), end diastolic (EDI) and cardiac contractility (IC) indices. Univariate analysis detected heritability estimates that ranged from 0.19–0.35 for rest, 0.002–0.40 for WCT and 0.08–0.35 for CPT.Conclusion:In this unique cohort, resting as well as challenged cardiovascular phenotypes are significantly influenced by additive genetic effects. Heritability estimates for resting phenotypes are in a relatively narrow range, while h2for their reactivity is somewhat broader with lower estimates. Further analyses of this study may offer important opportunities for gene finding in hypertension.What is Known About the Topic:(1) cardiovascular reactivity to stress predicts cardiovascular disease; (2) genetic susceptibility plays an important role in stress reactivity. Family studies using the cold pressure test reported significant heritability for blood pressure.What this Study Adds:(1) this cohort is from five highly consanguineous isolated Arab pedigrees with genetically verified genealogical records and environmental homogeneity; (2) This is the first study to estimate heritability of detailed intermediate hemodynamic phenotypes that make up normal blood pressure.

Plasma catecholamines, blood pressure responses and perceived stress during mental arithmetic stress in young men

We assessed plasma noradrenaline (NA) and adrenaline (A) at rest during a hyperinsulinaemic glucose clamp and responses to a mental arithmetic stress test (MST) in relation to blood pressure (BP) responses (Finapres) and distress in 20 men with high (> or =140/90 mmHg) and 21 men with normal (< or =115/75 mmHg) screening BP, 21-24 years of age. Perceived stress, effort and overall discomfort were scored 1-10. Catecholamines and BP increased in both groups, change in diastolic BP (DeltaDBP; 9.9 vs. 3.8 mmHg, p < 0.05) and DeltaDBP carryover (recovery period minus baseline) (7.2 vs. 2.2 mmHg, p < 0.01) being greater in men with high screening BP. Independently of BP status, change in systolic BP (DeltaSBP) and DeltaSBP carryover were related to A (both p < 0.001), and DeltaDBP and DeltaDBP carryover to DeltaNA (both p < 0.001). The subjective score sum correlated with maximal NA (rs = 0.40) and A (rs = 0.37) (both p < 0.05). Maximal NA was independently related to stress (p < 0.05) and the subjective score sum (p < 0.01). DeltaA% was greater in the high- (score > or =6) than in the low-stress category, independently of BP status (p < 0.05). High screening BP is associated with impaired BP recovery after mental stress. Plasma catecholamine responses are related to BP responses and carryover effects, and reflect perceived stress in young men.

Adrenaline during mental stress in relation to fitness, metabolic risk factors and cardiovascular responses in young men

We studied plasma adrenaline (A) in relation to physical fitness, metabolic cardiovascular risk factors and cardiovascular responses. Men (age 21-24 years) with high and normal (both n=19) screening blood pressure (BP) were studied cross-sectionally. We measured peak oxygen uptake (VO2peak) (treadmill exercise), and plasma catecholamines, heart rate (HR), finger systolic (SBP) and diastolic (DBP) BP, and insulin-adjusted glucose disposal rate (GDR/I) during a hyperinsulinaemic glucose clamp (rest) and mental arithmetic stress test (MST). By multiple regression, A at rest (Arest) (beta=0.37, p<0.05) and during MST (Amst) (beta=0.40, p<0.01) were associated with high screening BP. In the respective models, Arest was negatively related to body mass index (BMI) (beta=-0.56, p<0.001) and Amst positively to VO2peak (beta=0.54, p<0.001). BP and HR responses correlated positively with VO2peak, but were determined by Amst in multiple regression models. Independently of BMI and VO2peak, serum high-density lipoprotein cholesterol was positively related to A levels, whereas GDR/I was independently related only to VO2peak. Increased adrenaline secretion may be related to high BP, but may at the same time be associated with a beneficial metabolic profile.

Age-related memory impairments due to reduced blood glucose responses to epinephrine

Increases in blood glucose levels are an important component of the mechanisms by which epinephrine enhances memory formation. The present experiments addressed the hypothesis that a dysfunction in the blood glucose response to circulating epinephrine contributes to age-related memory impairments. Doses of epinephrine and glucagon that significantly increased blood glucose levels in young adult rats were far less effective at doing so in 2-year-old rats. In young rats, epinephrine and glucose were about equally effective in enhancing memory and in prolonging post-training release of acetylcholine in the hippocampus. However, glucose was more effective than epinephrine in enhancing both memory and acetylcholine release in aged rats. These results suggest that an uncoupling between circulating epinephrine and glucose levels in old rats may lead to an age-related reduction in the provision of glucose to the brain during training. This in turn may contribute to age-related changes in memory and neural plasticity.

Intestinal intraepithelial lymphocyte derived angiotensin converting enzyme modulates epithelial cell apoptosis

BACKGROUND & AIMS

Intestinal adaptation in short bowel syndrome (SBS) consists of increased epithelial cell (EC) proliferation as well as apoptosis. Previous microarray analyses of intraepithelial lymphocytes (IEL) gene expression after SBS showed an increased expression of angiotensin converting enzyme (ACE). Because ACE has been shown to promote alveolar EC apoptosis, we examined if IEL-derived ACE plays a role in intestinal EC apoptosis.

METHODS

Mice underwent either a 70% mid-intestinal resection (SBS group) or a transection (Sham group) and were studied at 7 days. ACE expression was measured, and ACE inhibition (ACE-I, enalaprilat) was used to assess ACE function.

RESULTS

IEL-derived ACE was significantly elevated in SBS mice. The addition of an ACE-I to SBS mice resulted in a significant decline in EC apoptosis. To address a possible mechanism, tumor necrosis factor alpha (TNF-alpha) mRNA expression was measured. TNF-alpha was significantly increased in SBS mice, and decreased with ACE-I. Interestingly, ACE-I was not able to decrease EC apoptosis in TNF-alpha knockout mice.

CONCLUSIONS

This study shows a previously undescribed expression of ACE by IEL. SBS was associated with an increase in IEL-derived ACE. ACE appears to be associated with an up-regulation of intestinal EC apoptosis. ACE-I significantly decreased EC apoptosis.

Ghrelin has novel vascular actions that mimic PI 3-kinase-dependent actions of insulin to stimulate production of NO from endothelial cells

Ghrelin is an orexigenic peptide hormone secreted by the stomach. In patients with metabolic syndrome and low ghrelin levels, intra-arterial ghrelin administration acutely improves their endothelial dysfunction. Therefore, we hypothesized that ghrelin activates endothelial nitric oxide synthase (eNOS) in vascular endothelium, resulting in increased production of nitric oxide (NO) using signaling pathways shared in common with the insulin receptor. Similar to insulin, ghrelin acutely stimulated increased production of NO in bovine aortic endothelial cells (BAEC) in primary culture (assessed using NO-specific fluorescent dye 4,5-diaminofluorescein) in a time- and dose-dependent manner. Production of NO in response to ghrelin (100 nM, 10 min) in human aortic endothelial cells was blocked by pretreatment of cells with NG-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor), wortmannin [phosphatidylinositol (PI) 3-kinase inhibitor], or (D-Lys3)-GHRP-6 (selective antagonist of ghrelin receptor GHSR-1a), as well as by knockdown of GHSR-1a using small-interfering (si) RNA (but not by mitogen/extracellular signal-regulated kinase inhibitor PD-98059). Moreover, ghrelin stimulated increased phosphorylation of Akt (Ser473) and eNOS (Akt phosphorylation site Ser1179) that was inhibitable by knockdown of GHSR-1a using siRNA or by pretreatment of cells with wortmannin but not with PD-98059. Ghrelin also stimulated phosphorylation of mitogen-activated protein (MAP) kinase in BAEC. However, unlike insulin, ghrelin did not stimulate MAP kinase-dependent secretion of the vasoconstrictor endothelin-1 from BAEC. We conclude that ghrelin has novel vascular actions to acutely stimulate production of NO in endothelium using a signaling pathway that involves GHSR-1a, PI 3-kinase, Akt, and eNOS. Our findings may be relevant to developing novel therapeutic strategies to treat diabetes and related diseases characterized by reciprocal relationships between endothelial dysfunction and insulin resistance.

Key role of the NO-pathway and matrix metalloprotease-9 in high blood flow-induced remodeling of rat resistance arteries

OBJECTIVE

Blood flow is altered in metabolic and ischemic diseases with dramatic consequences. Resistance arteries structure and function remodel in response to chronic blood flow changes through a mechanism remaining mainly unknown. We hypothesized that the NO pathway and matrix metalloproteases (MMPs) activation might play a role in flow (shear stress)-induced microvascular remodeling.

METHODS AND RESULTS

Mesenteric resistance arteries were ligated to alter blood flow in vivo for 4 or 14 days: arteries were submitted to high (HF), low (LF), or normal flow (NF). Rats were treated with L-NAME, the angiotensin converting enzyme inhibitor perindopril or the MMPs inhibitor doxycycline. After 14 days, outward hypertrophic remodeling occurred in HF arteries in association with eNOS overexpression. MMP9 activity increased in the early phase (day 4). HF-remodeling was prevented by L-NAME, eNOS gene knockout, and doxycycline. L-NAME prevented eNOS overexpression and MMPs activation whereas doxycycline only prevented MMPs activation. In LF arteries diameter reduction was associated with a decreased eNOS expression without change in MMPs expression and activation. LF-remodeling was reduced by perindopril.

CONCLUSIONS

In resistance arteries, high flow induced diameter enlargement and wall hypertrophy associated with the sequential activation of eNOS and MMP9.

Antihypertensive Potential and Mechanism of Action of Astaxanthin: III. Antioxidant and Histopathological Effects in Spontaneously Hypertensive Rats

We investigated the effects of a dietary astaxanthin (ASX-O) on oxidative parameters in spontaneously hypertensive rats (SHR), by determination of the level of nitric oxide (NO) end products nitrite/nitrate (NO2-/NO3-) and lipid peroxidation in ASX-O-treated SHR. Oral administration of the ASX-O significantly reduced the plasma level of NO2-/NO3- compared to the control vehicle (p<0.05). The lipid peroxidation level, however, was reduced in both ASX-O- and olive oil-treated groups. We also analyzed the post-treatment effects of ASX-O on the vascular tissues by examining the changes in the aorta and coronary arteries and arterioles. The dietary ASX-O showed significant reduction in the elastin bands in the rat aorta (p<0.05). It also significantly decreased the [wall : lumen] aerial ratio of the coronary arteries. These results suggest that ASX-O can modulate the oxidative condition and may improve vascular elastin and arterial wall thickness in hypertension.

Sympathetic nerve function--assessment by radioisotope dilution analysis

Radioisotope dilution measurements of norepinephrine spillover (rate of entry of the transmitter into plasma) provide more accurate assessments of sympathoneural transmitter release than allowed by measurements of plasma catecholamine concentrations alone. Measurements of total body norepinephrine spillover, as an index of global sympathetic outflow, allow effects on plasma clearance to be distinguished from effects on release of catecholamines into plasma, while spillovers from specific tissues enable examination of regionalized sympathetic responses. However, spillovers of norepinephrine represent only a fraction of the transmitter that escapes neuronal and extraneuronal uptake after release by nerves. Numerous factors may influence this fraction and measures spillovers independently of transmitter release by nerves. Modified radioisotope dilution methods for assessment of rate processes operating within and between intracellular and extracellular compartments have further improved our understanding of the relationships of norepinephrine release, uptake, spillover, turnover, and metabolism. This article reviews the breadth of information about sympathetic nerve function attainable using catecholamine radioisotope dilution analyses against a backdrop of the relative advantages and methodological limitations associated with the methodology.

Oxidative Stress Promotes Endothelial Cell Apoptosis and Loss of Microvessels in the Spontaneously Hypertensive Rats

OBJECTIVE

Endothelial cell apoptosis caused by oxidative stress may lead to the loss of microvessels (rarefaction) in hypertension. We examine here the effects of antioxidants on cell apoptosis and rarefaction.

METHODS AND RESULTS

The juvenile spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were treated with superoxide scavengers, Tempol or Tiron, during growth. After the treatment, oxidative stress status, endothelial cell apoptosis rate, and microvessel length density in skeletal muscle and mesentery were evaluated in comparison with age-matched controls. Untreated 16-week-old SHR had higher oxidative stress (P<0.01) and cell apoptosis rate (P<0.05) and lower microvessel length density (371+/-17 mm/mm3 [P<0.01]) compared with age-matched WKY rats (435+/-15 mm/mm3). In the SHR, but not in WKY rats, systemically applied antioxidants attenuated oxidative stress and cell apoptosis rate (P<0.05 versus untreated controls) and prevented the loss of microvessels (411+/-15 mm/mm3 for Tempol [P<0.01 versus untreated control] and 399+/-17 mm/mm3 for Tiron [P<0.05]).

CONCLUSIONS

Antioxidant treatment with cell-permeable superoxide scavengers inhibits endothelial cell apoptosis and prevents microvessel rarefaction in the SHR during growth.

Reduced Vascular Remodeling, Endothelial Dysfunction, and Oxidative Stress in Resistance Arteries of Angiotensin II–Infused Macrophage Colony-Stimulating Factor–Deficient Mice

OBJECTIVE

Angiotensin (Ang) II-induced vascular damage may be partially mediated by reactive oxygen species generation and inflammation. Homozygous osteopetrotic mice (Op/Op), deficient in macrophage colony-stimulating factor (m-CSF), exhibit reduced inflammation. We therefore investigated Ang II effects on vascular structure, function, and oxidant stress generation in this model.

METHODS AND RESULTS

Adult Op/Op, heterozygous (Op/+), and wild type (+/+) mice underwent 14-day Ang II (1000 ng/kg per minute) or saline infusion. Blood pressure (BP) was assessed by radiotelemetry, mesenteric resistance artery vascular reactivity was studied on a pressurized myograph, and vascular superoxide and NAD(P)H oxidase activity by lucigenin chemiluminescence. Ang II increased BP in Op/+ and +/+ mice but not in Op/Op. Ang II-treated Op/+ and +/+ mice showed reduced acetylcholine-mediated relaxation (maximal relaxation, respectively, 64% and 67% versus 84% and 93% in respective controls; P<0.05), which was unaffected by L-NAME. Ang II-infused Op/Op mice arteries showed significantly less endothelial dysfunction than vehicle-infused counterparts (maximal relaxation 87% versus 96% in shams). Resistance arteries from Ang II-infused +/+ and Op/+ mice had significantly increased media-to-lumen ratio and media thickness, neither of which was altered in Op/Op mice compared with untreated littermates. Vascular media cross-sectional area, NAD(P)H oxidase activity and expression, and vascular cell adhesion molecule (VCAM)-1 expression were significantly increased by Ang II only in +/+ mice (P<0.05).

CONCLUSIONS

m-CSF-deficient mice (Op/Op) developed less endothelial dysfunction, vascular remodeling, and oxidative stress induced by Ang II than +/+ littermates, suggesting a critical role of m-CSF and proinflammatory mediators in Ang II-induced vascular injury.

Relationship between noradrenaline and nonlinear indexes of blood pressure dynamics in normotensive and spontaneously hypertensive rats

Recent studies in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats show that some nonlinear indexes derived from the recurrence plot method may be better markers of sympathetic activity than the spectral powers of blood pressure (BP). We herein investigated the relationships between nonlinear indexes and plasma noradrenaline concentration in conscious WKY rats and SHRs. Blood pressure was recorded for 30 min after intravenous injection of saline (0.9% NaCl, 100 microL/kg), hexamethonium (20 mg/kg), atropine (0.5 mg/kg), atenolol (1 mg/kg) or prazosin (1 mg/kg). Spectral power in the low-frequency (LF) band and the nonlinear index (L(max)), calculated on diastolic (DBP) and systolic blood pressures (SBP), were used to analyse the BP signal. Noradrenaline concentration was determined by radioenzymatic technique. A robust stepwise regression analysis - using noradrenaline concentration as dependent variable, and LF, L(max) and treatment, as independent variables -shows that treatment is the main variable explaining the variance of noradrenaline level in WKY rats, excluding the use of the pooled data to explore the relationship between noradrenaline concentration and LF or L(max). In contrast, in SHRs, treatment has no effect on the variance of noradrenaline concentration and the pooled data were then used. In this group, no correlation was observed between noradrenaline concentration and LF. In contrast, very high positive correlation was observed between noradrenaline level and L(max)-DBP (r = 0.59; P = 0.0005) or L(max)-SBP (r = 0.53; P < 0.002). The results strengthen our previous suggestion that nonlinear indexes may be better tools than spectral powers to investigate the sympathetic nervous system.

Role of the newer alpha, -adrenergic-receptor antagonistsin the treatment of benign prostatic hyperplasia-related lower urinary tract symptoms

BACKGROUND

Although initially introduced for the management of hypertension, alpha(1)-adrenergic-receptor antagonists (alpha1-blockers) have become the standard of care for the medical management of benign prostatic hyperplasia (BPH)-related lower urinary tract symptoms (LUTS). However, these agents have the potential to produce orthostatic hypotension and other blood pressure-related adverse effects in normotensive patients and in those receiving concurrent treatment with other antihypertensive agents. As a result, more "uroselective," less vasoactive alpha(1)-blockers have been developed.

OBJECTIVE

This article reviews current information on the role of alpha(1)-blockers in the treatment of BPH-related LUTS. The focus is on tamsulosin and alfuzosin, newer "uroselective" agents in this class that have a decreased potential for cardiovascular adverse effects.

METHODS

Relevant articles were identified through a search of the English-language literature indexed on MEDLINE and the proceedings of scientific meetings from 1976 to 2003. The search terms were benign prostatic hyperplasia treatment, alpha(1)-adrenergic-receptor blocker, uroselectivity, lower urinary tract symptoms, complications, and cardiovascular.

RESULTS

Tamsulosin has selectivity for the a alpha(1) and alpha(1d) receptor subtypes. Alfuzosin, although not receptor subtype selective, is clinically "uroselective" and does not significantly affect vascular alpha-adrenergic receptors. Both agents are efficacious in relieving LUTS and have a decreased potential for such cardiovascular adverse effects as postural hypotension. Common adverse events with these agents include dizziness and asthenia.

CONCLUSION

Based on the available data, "uroselective" alpha(1)-blockers should be considered over older, more vasoactive agents for the medical management of LUTS, particularly in patients with BPH and hypertension.

Lower body negative pressure as a model to study progression to acute hemorrhagic shock in humans

Hemorrhage is a leading cause of death in both civilian and battlefield trauma. Survival rates increase when victims requiring immediate intervention are correctly identified in a mass-casualty situation, but methods of prioritizing casualties based on current triage algorithms are severely limited. Development of effective procedures to predict the magnitude of hemorrhage and the likelihood for progression to hemorrhagic shock must necessarily be based on carefully controlled human experimentation, but controlled study of severe hemorrhage in humans is not possible. It may be possible to simulate hemorrhage, as many of the physiological compensations to acute hemorrhage can be mimicked in the laboratory by applying negative pressure to the lower extremities. Lower body negative pressure (LBNP) sequesters blood from the thorax into dependent regions of the pelvis and legs, effectively decreasing central blood volume in a similar fashion as acute hemorrhage. In this review, we compare physiological responses to hemorrhage and LBNP with particular emphasis on cardiovascular compensations that both share in common. Through evaluation of animal and human data, we present evidence that supports the hypothesis that LBNP, and resulting volume sequestration, is an effective technique to study physiological responses and mechanisms associated with acute hemorrhage in humans. Such experiments could lead to clinical algorithms that identify bleeding victims who will likely progress to hemorrhagic shock and require lifesaving intervention(s).

Prognostic significance of small-artery structure in hypertension

BACKGROUND

The presence of structural alterations in the microcirculation may be considered an important mechanism of organ damage; however, it is not currently known whether structural alterations of small arteries may predict fatal and nonfatal cardiovascular events.

METHODS AND RESULTS

One hundred twenty-eight patients were included in the present study. There were 59 patients with essential hypertension, 17 with pheochromocytoma, 20 with primary aldosteronism, 12 with renovascular hypertension, and 20 normotensive patients with non-insulin-dependent diabetes mellitus. All subjects were submitted to a biopsy of subcutaneous fat. Small resistance arteries were dissected and mounted on an isometric myograph, and the tunica media-to-internal lumen ratio (M/L) was measured. The subjects were reevaluated after an average follow-up time of 5.4 years. Thirty-seven subjects had a documented fatal or nonfatal cardiovascular event (5.32 events/100 patients per year). In the subcutaneous small arteries of subjects with cardiovascular events, a smaller internal diameter and a clearly greater M/L was observed. Our subjects were subdivided according to the presence of an M/L greater or smaller than the mean and median values observed in the whole population (0.098) or mean value +2 SD of our normal subjects (0.11). Life-table analyses showed a significant difference in event-free survival between the subgroups. Cox's proportional hazard model, considering all known cardiovascular risk factors, indicated that only pulse pressure (P=0.009) and M/L (P<0.0001) were significantly associated with the occurrence of cardiovascular events.

CONCLUSIONS

Our results strongly indicate a relevant prognostic role of structural alterations in small resistance arteries of a high-risk population.

Brain renin-angiotensin system dysfunction in hypertension: recent advances and perspectives

This review focuses on the dysfunction of the intrinsic brain renin-angiotensin system (RAS) in the pathogenesis of hypertension. Hyperactivity of the brain RAS plays a critical role in mediating hypertension in both humans and animal models of hypertension, including the spontaneously hypertensive rat (SHR). The specific mechanisms by which increased brain RAS activity results in hypertension are not well understood but include increases in sympathetic vasomotor tone and impaired arterial baroreflex function. We discuss the contribution of endogenous angiotensin (Ang) II actions on presympathetic vasomotor rostral ventrolateral medulla neurons to enhance sympathetic activity and maintain hypertension. In addition, we discuss Ang II-induced attenuation of afferent baroreceptor feedback within the nucleus tractus solitarius and its relevance to the development of hypertension. We also outline the cellular and molecular mechanisms of Ang II signal transduction that may be critical for the initiation and establishment of hypertension. In particular, we present evidence for a phosphoinositide-3-kinase-dependent signaling pathway that appears to contribute to hypertension in the SHR, possibly via augmented Ang II-induced increases in neuronal firing rate and enhanced transcriptional noradrenaline neuromodulation. Finally, we outline future directions in utilizing our understanding of the brain RAS dysfunction in hypertension for the development of improved therapeutic intervention in hypertension.

Sympathetic activation in human heart failure: diverse mechanisms, therapeutic opportunities

Plasma noradrenaline (NA) concentrations relate both to the severity of heart failure, and to its impact on survival, but have shortcomings that limit their usefulness as measures of sympathetic discharge. Neural recordings and the isotopic dilution method for determining organ-specific rates of NA spillover into plasma have enhanced our understanding of mechanisms responsible for sympathetic activation. Because the arterial baroreceptor reflex control of heart rate is impaired in heart failure, a parallel reduction in the reflex inhibition of sympathetic outflow has been assumed. However, human heart failure is characterized by rapidly responsive arterial baroreflex regulation of muscle sympathetic nerve activity (MSNA), attenuated cardiopulmonary reflex modulation of MSNA, and activation of a cardiac-specific sympatho-excitatory reflex related to increased cardiopulmonary filling pressures. Together, these baroreceptor mediated mechanisms account only, in part, for the time course and magnitude of adrenergic activation in heart failure. Non-baroreflex sympatho-excitatory mechanisms include: a metaboreflex arising from exercising skeletal muscle, mediated, in part, by adenosine, co-existing sleep apnoea, and pre-junctional facilitation of NA release. Thus, sympathetic activation in the setting of impaired systolic function reflects the net balance and interaction between augmented excitatory and diminished inhibitory influences. Variation, between patients, in the dynamics, magnitude and progression of sympathetic activation mandates an individualized approach to investigation and therapy. Excessive sympathetic outflow to the heart and periphery can be addressed by several complimentary strategies: attenuating these sympatho-excitatory stimuli, modulating the neural regulation of NA release, and blocking the actions of catecholamines at post-junctional receptors.

Spironolactone improves angiotensin-induced vascular changes and oxidative stress

Angiotensin II plays an important role in vascular remodeling. We investigated the role of aldosterone, which is stimulated by angiotensin II, as a mediator of angiotensin II-induced vascular structural and functional alterations. Sprague-Dawley rats (n=8 to 12/group) received angiotensin II (120 ng/kg per minute, subcutaneously) for 14 days +/- spironolactone or hydralazine (25 mg/kg per day). An additional group received aldosterone (750 ng/h, subcutaneously) +/- spironolactone. Systolic blood pressure was increased by angiotensin II (P<0.001) and reduced by spironolactone and hydralazine (P<0.001). Aldosterone-induced increase of blood pressure was reduced by spironolactone (P<0.05). In mesenteric small arteries studied on a pressurized myograph, media/lumen ratio was increased (P<0.001) and acetylcholine-mediated relaxation was impaired in angiotensin II-infused rats (P<0.001); both were partially improved by spironolactone (P<0.05) but not by hydralazine. Aldosterone-induced increase of media/lumen ratio (P<0.001) and impaired response to acetylcholine (P<0.001) were normalized by spironolactone. Response to sodium nitroprusside was similar in all groups. Aortic NADPH oxidase activity was increased (P<0.01) by angiotensin II and reduced by spironolactone and hydralazine. Aldosterone also increased (P<0.05) activation of NADPH oxidase, an effect abolished by spironolactone. Plasma thiobarbituric acid-reactive substances (a marker of oxidative stress), higher in angiotensin II and aldosterone rats (P<0.001), were normalized by spironolactone. In conclusion, spironolactone, which inhibited aldosterone actions, partially corrected structural and functional angiotensin II-induced abnormalities. These effects were associated with reduced vascular NADPH oxidase activity and decreased plasma markers of oxidative stress. Our findings suggest that aldosterone may mediate some of angiotensin II-induced vascular effects in hypertension, in part via increased oxidative stress.

Role of the alpha1D-adrenergic receptor in the development of salt-induced hypertension

In an attempt to elucidate whether there is a specific alpha1-adrenergic receptor (alpha1-AR) subtype involved in the genesis or maintenance of hypertension, the alpha1D-AR subtype was evaluated in a model of salt-induced hypertension. The alpha1D-AR-deficient (alpha1D-/-) and control (alpha1D+/+) mice (n=8 to 14 in each group) were submitted to subtotal nephrectomy and given 1% saline as drinking water for 35 days. Blood pressure (BP) was monitored by tail-cuff readings and confirmed at the end point by direct intraarterial BP recording. The alpha1D-/- mice had a significantly (P=0.0004) attenuated increase in BP response in this protocol (baseline 94.6+/-2.8 versus end point 107.4+/-4.5 mm Hg) compared with that of their wild-type counterparts (alpha1D+/+), from a baseline 97.4+/-2.9 to an end point 139.4+/-4.5 mm Hg. Seven of 15 alpha1D+/+ mice died with edema, probably owing to renal failure, whereas 14 of 15 alpha1D-/- mice were maintained for 35 days. Body weight, renal remnant weight, and residual renal function were similar in the 2 groups, whereas the values of plasma catecholamines (epinephrine, norepinephrine, and dopamine) were higher in alpha1D+/+ than in the alpha1D-/- mice. These data suggest that alpha1D-AR plays an important role in developing a high BP in response to dietary salt-loading, and that agents having selective alpha1D-AR antagonism could have significant therapeutic potential in the treatment of hypertension.

Altered nitric oxide synthase 3 distribution in mesenteric arteries of hypertensive rats

A high-salt (HS) diet and angiotensin II (Ang II) are both associated with the development of hypertension and impaired endothelial function. We hypothesize that alterations in nitric oxide synthase (NOS) activity or subcellular localization of NOS 3 protein may contribute to endothelial dysfunction in salt-dependent hypertension. To test this hypothesis, two models of salt-dependent hypertension were studied: DOCA-salt and Ang II. For Ang II hypertension, rats were divided into 4 groups: control on normal or HS diet, Ang II-infused on normal or HS diet. The mesenteric arterial bed was isolated and frozen in liquid nitrogen. Frozen arteries were homogenized and separated into cytosolic and particulate fractions. NOS activity was assayed by determining the conversion of (3)H-arginine to (3)H-citrulline in the absence and presence of the NOS inhibitor, Nomega-nitro-L-arginine. NOS 3 protein expression was significantly increased in the cytosol of arteries from DOCA-salt compared with placebo rats and in Ang II-infused and Ang HS rats compared with control. NOS 3 expression in the particulate fraction was comparable among all groups. NOS activity (pmol/30 min/total protein) was significantly increased in the cytosolic fraction of arteries from DOCA-salt rats compared with placebo and in Ang HS rats compared with control. NOS activity was comparable in the particulate fraction in all rat groups. In conclusion, there is an altered subcellular distribution of NOS 3 in salt-dependent hypertension that may contribute to the development of hypertension and endothelial dysfunction.

Chronic treatment with a superoxide dismutase mimetic prevents vascular remodeling and progression of hypertension in salt-loaded stroke-prone spontaneously hypertensive rats

Oxidative stress has been implicated in the pathogenesis of hypertension. The aim of the present study was to determine whether increased generation of vascular superoxide anion (*O2-) contributes to blood pressure elevation by influencing vascular function and structure in severely hypertensive rats. Sixteen-week-old stroke-prone spontaneously hypertensive rats (SHRSP) (n = 12) were randomly divided into two groups to receive the superoxide dismutase mimetic, tempol (4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl) (1 mmol/L in drinking water) or tap water. Both groups were fed a high-salt diet (4% NaCl). Systolic blood pressure (SBP) was measured weekly for 6 weeks by the tail-cuff method. Rats were killed, and vascular structure (media:lumen ratio) and endothelial function (acetylcholine [Ach]-induced vasodilation) were assessed in small mesenteric arteries mounted as pressurized preparations. Vascular *O2- concentration was measured by lucigenin (5 micromol/L) chemiluminescence. Plasma total antioxidant status was assessed spectrophotometrically. The SBP increased significantly (P < .01) in the control group, whereas progression of hypertension was prevented in the tempol-treated group. Tempol reduced (P < .01) the media:lumen ratio (7.2%+/-0.01%) compared with that in controls (12.0%+/-0.01%). Maximal Ach-induced dilation was altered in control rats (40%+/-9%) but was not influenced by tempol (57%+/-17%). Vascular *O2- concentration was lower (P < .01) and plasma total antioxidant concentration was higher (P < .05) in the treated group compared with the control. In conclusion, tempol prevents progression of hypertension. These processes are associated with attenuated vascular remodeling, decreased vascular *O2- concentration, and increased antioxidant status. Our data suggest that oxidative stress plays an important role in vascular damage associated with severe hypertension in salt-loaded SHRSP.

Sympathetic nerve biology in essential hypertension

1. Although the importance of sympathetic nervous activation in the pathogenesis of essential hypertension is well documented, the exact pathophysiology of the sympathetic nervous dysfunction present remains to be delineated. There are several possible explanations for the increased spillover of noradrenaline from the kidneys and heart to plasma, a key piece of evidence supporting the neurogenic basis of essential hypertension, in addition to the obvious one of an increased rate of sympathetic nerve firing. 2. The possibility that there may be an increase in the density of sympathetic innervation in human hypertension, well documented in the spontaneously hypertensive rat, is currently under investigation by us. 3. Adrenaline cotransmission is present in the cardiac sympathetic nerves of patients with essential hypertension, presumptive evidence of their exposure to high levels of stress and a possible basis for the observed increase in cardiac noradrenaline spillover, through presynaptic augmentation of noradrenaline release. 4. Phenotypic evidence exists also of faulty noradrenaline reuptake into the sympathetic nerves of the heart in essential hypertension, an abnormality that would amplify the sympathetic neural signal by impairing removal of noradrenaline from the synaptic cleft.

Effect of a COL1A1 Sp1 binding site polymorphism on arterial pulse wave velocity: an index of compliance

-Reduced arterial compliance precedes changes in blood pressure, which may be mediated through alterations in vessel wall matrix composition. We investigated the effect of the collagen type I-alpha1 gene (COL1A1) +2046G>T polymorphism on arterial compliance in healthy individuals. We recruited 489 subjects (251 men and 238 women; mean age, 22.6+/-1.6 years). COL1A1 genotypes were determined using polymerase chain reaction and digestion by restriction enzyme Bal1. Arterial pulse wave velocities were measured in 3 segments, aortoiliac (PWVA), aortoradial (PWVB), and aorto-dorsalis-pedis (PWVF), as an index of compliance using a noninvasive optical method. Data were available for 455 subjects. The sample was in Hardy-Weinberg equilibrium with genotype distributions and allele frequencies that were not significantly different from those reported previously. The T allele frequency was 0.22 (95% confidence interval, 0.19 to 0.24). Two hundred eighty-three (62.2%) subjects were genotype GG, 148 (35.5%) subjects were genotype GT, and 24 (5.3%) subjects were genotype TT. A comparison of GG homozygotes with GT and TT individuals demonstrated a statistically significant association with arterial compliance: PWVF 4.92+/-0.03 versus 5.06+/-0.05 m/s (ANOVA, P=0.009), PWVB 4.20+/-0.03 versus 4.32+/-0.04 m/s (ANOVA, P=0.036), and PWVA 3.07+/-0.03 versus 3.15+/-0.03 m/s (ANOVA, P=0.045). The effects of genotype were independent of age, gender, smoking, mean arterial pressure, body mass index, family history of hypertension, and activity scores. We report an association between the COL1A1 gene polymorphism and arterial compliance. Alterations in arterial collagen type 1A deposition may play a role in the regulation of arterial compliance.

Quantification of Unconjugated Metanephrines in Human Plasma without Interference by Acetaminophen

Background: Pheochromocytoma is a rare cause of hypertension resulting from increased catecholamine secretion. We aimed to develop a method to measure unconjugated plasma normetanephrine (NMN) and metanephrine (MN) without interference from acetaminophen, a widely prescribed drug for headaches.

Methods: Plasma samples were obtained from 48 subjects (23 males, 25 females; mean age, 49 ± 14 years; hypertension, n = 37) under resting conditions. Following extraction on solid-phase cation-exchange columns, unconjugated metanephrines were analyzed by HPLC with electrochemical detection and with 4-hydroxy-3-methoxybenzylamine as an internal standard. Catecholamines were measured by HPLC.

Results: The assays were linear up to 2000 pg for NMN and for MN. Intraassay imprecisions (CVs) were 4.7% for NMN and 7.0% for MN, and the interassay CV was 12% for both NMN and MN. The limit of detection was 11 fmol for NMN and 17 fmol for MN. Ingestion of acetaminophen or its addition to plasma did not interfere with the MN peaks. Plasma NMN and MN were positively correlated (r = 0.52 and 0.49, respectively; P &lt;0.01 for both) with the respective catecholamines. Plasma NMN (r = 0.27; P = 0.02) but not MN positively correlated with age, whereas only plasma catecholamines (and not metanephrines) were positively correlated (P &lt;0.05) with diastolic blood pressure.

Conclusions: This sensitive MN assay is not affected by simultaneous acetaminophen medication, and reveals a correlation of metanephrines with plasma and urinary catecholamines and age but not with blood pressure.

Phenotypic evidence of faulty neuronal norepinephrine reuptake in essential hypertension

Previous reports suggest that neuronal norepinephrine (NE) reuptake may be impaired in essential hypertension, perhaps because of dysfunction of the NE transporter, although the evidence is inconclusive. To further test this proposition, we applied phenotypically relevant radiotracer methodology, infusion of tritiated NE and quantification of NE metabolites, to 34 healthy lean subjects (body mass index <27.0 kg/m(2)), 19 overweight (body mass index >28.0 kg/m(2)) but otherwise healthy normotensive subjects, 13 untreated lean patients with essential hypertension, and 14 obesity-related hypertensives. Spillover of NE from the heart was increased in lean hypertensives only (mean+/-SD 33.4+/-20.6 versus 16.1+/-11.7 ng/min in lean normotensives, P<0.05), but this could have resulted from high cardiac sympathetic nerve firing rates, faulty NE reuptake, or both. The arterial plasma concentration of 3-methoxy-4-hydroxylphenylglycol, an extraneuronal metabolite of NE, was elevated in lean hypertensives only (3942+/-1068 versus 3055+/-888 pg/mL in healthy subjects, P:<0.05). The fractional extraction of plasma tritiated NE in passage through the heart, determined on the basis of neuronal NE uptake, was reduced in lean essential hypertensives (0.65+/-0.19 versus 0.81+/-0.11 in healthy subjects, P<0.05). Cardiac release of the tritiated NE metabolite [(3)H]dihydroxylphenylglycol, produced intraneuronally by monoamine oxidase after uptake of [(3)H]NE by the transporter, was reduced in lean hypertensives only (992+/-1435 versus 4588+/-3189 dpm/min in healthy subjects, P<0.01) These findings suggest that neuronal reuptake of NE is impaired in essential hypertension. Through amplification of the neural signal, such a defect could constitute a neurogenic variant of essential hypertension. In obesity-related hypertension, there was no phenotypic evidence of NE transporter dysfunction.

An overview of essential hypertension in Americans as a multifactorial phenomenon: interaction of biologic and environmental factors

This paper reviews the current literature on essential/primary hypertension in terms of its expression as a multifactorial phenomenon. The genetic and environmental risk factors involved in expression of hypertension and their interactions are discussed. A specific mutation in epithelial sodium channels, T549M, is presented as a genetic risk factor for primary hypertension as expression of this mutation has been reported to result in hyperabsorption of sodium in homozygous individuals. T549M is used in this report to illustrate the multifactorial nature of primary hypertension. Possible interactions of T549M with environmental factors known to promote hypertension and the outcome of these interactions are discussed. Data indicates that both genetic and environmental risk factors must be considered to understand and intervene effectively with patients who have primary or essential hypertension.

The 'adrenaline hypothesis' of hypertension revisited: evidence for adrenaline release from the heart of patients with essential hypertension

OBJECTIVE

Whether adrenaline acts as a sympathetic nervous cotransmitter in humans and stimulates beta2-adrenoceptors to augment neuronal noradrenaline release remains a subject of considerable dispute. The aim of this study was to test if adrenaline is released from regional sympathetic nerves (in the heart) in patients with essential hypertension, and to investigate whether locally released adrenaline might enhance cardiac noradrenaline release.

METHODS

Using dual isotope dilution methodology, adrenaline and noradrenaline plasma kinetics was measured for the whole body and in the heart in 13 untreated patients with essential hypertension and 27 healthy volunteers. All research participants underwent cardiac catheterization under resting conditions.

RESULTS

At rest, there was negligible adrenaline release from the sympathetic nerves of the heart in healthy subjects, 0.27 +/- 1.62 ng/min. In contrast, in patients with essential hypertension, adrenaline was released from the heart at a rate of 1.46 +/- 1.73 ng/min, equivalent on a molar basis to approximately 5% of the associated cardiac noradrenaline spillover value. Cardiac noradrenaline spillover was higher in hypertensive patients, 24.9 +/- 17.0 ng/min compared to 15.4 +/- 11.7 ng/min in healthy volunteers (P< 0.05). Among patients, rates of cardiac adrenaline and noradrenaline spillover correlated directly (r= 0.59, P< 0.05).

CONCLUSIONS

This study, in demonstrating release of adrenaline from the heart in patients with essential hypertension, and in disclosing a proportionality between rates of cardiac adrenaline and noradrenaline release, provides perhaps the most direct evidence to date in support of the 'adrenaline hypothesis' of essential hypertension.

As human pial arteries (internal diameter 200-1000 microm) get smaller, their wall thickness and capacity to develop tension relative to their diameter increase

Pial arteries play a key role in the regulation of human cerebral blood flow. However, many of the features and mechanisms that regulate the tone and diameters of these vessels cannot be studied in situ. One approach is to study in vitro segments of arteries obtained during neurosurgical procedures. The ratios of arterial media thickness to lumen diameter and of the capacity to develop wall force to lumen diameter have important functional consequences and are known to change in disease. Experiments were carried out on pial arteries from normotensive humans to determine the way in which these parameters vary with vessel size. Vessel dimensions--media thickness and lumen diameter were derived from fixed sections using quantitative morphometry. Wall force was measured using a resistance artery myograph. The ratio of media thickness to lumen diameter and of maximum tension developed to lumen diameter both increased as vessel diameter decreased. These ratios do not change over the age range of 15-75 years. These findings show that although in vivo intralumenal pressure falls as human pial arteries become smaller, their media thickness and capacity to develop tone increase.